A rubber crawler is entrained about driving wheels and idle wheels provided at a vehicle main body, and used for running the vehicle. However, usually, a row of reinforcing tension members (hereinafter referred to as a main cord row) such as a row of steel cords is embedded in a rubber crawler in the longitudinal direction thereof, and two layers of bias cords, having opposite bias angles, are simultaneously embedded at an outer peripheral side of the main cord row. These bias cords exist to allow more smooth rotation or to prevent a crack from reaching the main cord row even when the crack occurs in a rubber part.
However, some problems do occur due to the bias cords being embedded in the rubber crawler, and there has been pointed out the disadvantage that bias cords (of a second layer) embedded at a position more remote, than bias cords of a first layer, with respect to the main cord row that serves as a neutral position of rotation, exhibits larger sheer stress than the bias cords of the first layer, thereby the rubber crawler causing the vehicle to run slantingly.
This effect is particularly distinct when the rubber crawler is entrained about driving wheels and rotated, resulting in the rubber crawler running slantingly. This tendency occurs significantly in the case of rubber crawlers having a small widthwise dimension. To this end, in conventional methods, the vehicle main body is equipped with an alignment mechanism for adjusting tension. In this alignment mechanism, adjustment must be carried out every time each rubber crawler is mounted in the vehicle main body.
In a case in which such alignment adjustment is not carried out, one-sided driving of the rubber crawler may occur, and partial abrasion of rubber that forms the rubber crawler may occur at an early stage, thereby resulting in a short-lived rubber crawler. Further, in some cases, such rubber crawlers may frequently come off of wheels.
In order to deal with the aforementioned problems, as a rubber crawler structure, a technique using the alignment mechanism as described above without consideration of neutralization of shear stress needs to be provided, or it is necessary that the bias cords in the first layer and the bias cords in the second layer should have different bias angles, or that the number of bias cords per unit width should be changed, or that the width of a bias cord row in the second layer is made smaller than that in the first layer, as disclosed in Japanese National Phase Publication (JP-T) No. 63-502978. However, these techniques also present various problems.
Specifically, when a structure in which the angles of bias cord rows are changed is used, although some effects are obtained, plural types of bias cords are required, and management of the operation process becomes extremely important. As a result, the workability may significantly deteriorate. Similarly, even in the technique of changing the number of bias cords per unit width, the types of bias cords may increase and management thereof becomes difficult. As a result, there is a high possibility that the bias cords to be used may be mistaken.
Moreover, in the technique in which the width of the bias cords in the second layer is made smaller, the rigidity of a transverse-direction end of a rubber crawler to be produced, that is, an edge portion of the rubber crawler, becomes low. When the rubber crawler thus formed is used for running the vehicle, edge deflection caused by running on projections or the like on a road surface occurs repeatedly. As a result, there arises a problem that rubber cracking is caused by the edge deflection, for example.